LOUISIANA DEPARTMENT OF WILDLIFE & FISHERIES

Transcription

1 LOUISIANA DEPARTMENT OF WILDLIFE & FISHERIES OFFICE OF FISHERIES INLAND FISHERIES SECTION PART VI -B WATERBODY MANAGEMENT PLAN SERIES HENDERSON LAKE WATERBODY EVALUATION & RECOMMENDATIONS

2 CHRONOLOGY DOCUMENT SCHEDULED TO BE UPDATED ANNUALLY May 7 - Prepared by Jody T. David, Biologist Manager, District 6 January 12 Vegetation recommendations updated by Mike Walker, Biologist Manager, District 9 February 14 - Updated by Brac Salyers, Biologist Manager, District 9 August 14 Updated by Brac Salyers, Biologist Manager, District 9 Remainder of this page left intentionally blank. 2

3 TABLE OF CONTENTS WATERBODY EVALUATION... 4 STRATEGY STATEMENT... 4 Recreational... 4 Commercial... 4 Species of Special Concern... 4 EXISTING HARVEST REGULATIONS... 4 Recreational... 4 Commercial... 4 SPECIES EVALUATION... 4 HABITAT EVALUATION Aquatic Vegetation CONDITION IMBALANCE / PROBLEM CORRECTIVE ACTION NEEDED RECOMMENDATIONS REFERENCES... 3

4 WATERBODY EVALUATION STRATEGY STATEMENT Recreational Black bass, crappie, and catfish in Henderson Lake are managed to provide anglers the greatest opportunity to catch and harvest a limit of fish. Sunfish are managed to provide a sustainable population while providing anglers the opportunity to catch and harvest numbers of fish. Commercial Commercial species of fish are managed to provide a sustainable population. Species of Special Concern No threatened or endangered fish species have been documented in this waterbody. EXISTING HARVEST REGULATIONS Recreational The Louisiana Wildlife and Fisheries Commission amended a rule to repeal the 14 inch minimum length limit (MLL) on black bass in the Atchafalaya Basin and adjacent waters. Effective June, 13, the new regulations are a 7 fish daily creel limit with no MLL. This regulation will remain in effect for two years at which time the area will revert to the statewide regulation of 1 black bass with no MLL. Black Bass no minimum length limit, 7 daily bag limit (bag limit in effect for 2 years, starting June, 13. After 2-year period, bag limit goes to 1 fish.) Statewide regulations for all fish species except black bass may be viewed at the link below: Commercial The commercial fishing regulations may be viewed at the link below: SPECIES EVALUATION Recreational Electrofishing is the most commonly used sampling technique to assess largemouth bass (LMB) relative abundance (catch per unit effort = CPUE), size distribution, and relative weight (physical body condition). Data collected during fall electrofishing is used to describe population trends, age composition, growth rate and mortality rate. The water in Henderson Lake is typically under influence from the Atchafalaya River in the springtime. High, turbid waters are an inconsistent influence to sampling. For that reason, electrofishing sampling is conducted in the fall only. 4

5 Number of LMB per hour Largemouth Bass Relative abundance, size structure indices and length distribution Electrofishing catch per unit effort (CPUE) fluctuated significantly from 1988 through 1997 (Figure 1). The total catch rates for 1988 and 1989 were below 5 LMB per hour, while the average for 1992 and 1993 were over 15 an hour. The numbers declined again over the next two years and sharply increased the following two years. Results depicted in Figure 2 show LMB catch rates to be highly variable. In relation to total CPUE, catch rates of individual size classes provide a more detailed description of the variations Figure 1. The mean total CPUE (+ SE) for largemouth bass collected from Henderson Lake, LA during fall electrofishing ( ). 5

6 Number of LMB per hour Figure 2. The mean total CPUE (+ SE) for largemouth bass collected from Henderson Lake, LA during fall electrofishing (3-13). Catch indices in Figure 3 clearly show a sharp peak in reproduction (substock-size) in 1993 following Hurricane Andrew. Stock-size bass continued to increase with each successive year. The discovery of hydrilla in 1994 is associated with an upward trend of bass. In Figure 4, a strong sub-stock size class can be seen in 3 subsequent to Hurricane Lili related fish kills. Lower catch rates for 6, 7, and 9 are likely related to the series of fish kills resulting from Hurricanes Rita (5) and Gustav and Ike (8). The increased abundance observed in the 1 sample reflects natural recovery from storm related fish kills. 6

7 Number of LMB per hour Number of LMB per hour Substock Stock Quality Preferred Figure 3. The CPUE for sub-stock, stock, quality and preferred size largemouth bass collected from Henderson Lake, LA during fall electrofishing ( ) Substock Stock Quality Preferred Figure 4. The CPUE for sub-stock, stock, quality and preferred size largemouth bass collected from Henderson Lake, LA during fall electrofishing (3-13). 7

8 Number of LMB per hour Results from 13 sampling represent current largemouth bass size distribution for Henderson Lake (Figure 5). Young-of-the-year (YOY) bass (3 to 6 inches) represent 38% of the sample. Stock and quality-size bass (8 to 14 inches) represent 43% of the sample. Bass greater than 14 inches represent only 3% of the sample Inch Groups Figure 5. Size distribution (inch groups) of largemouth bass collected during one hour of electrofishing effort at Henderson Lake, LA in fall 13 (n=176). Proportional stock density (PSD) and relative stock density (RSD) are indices used to numerically describe length-frequency data (Anderson and Neumann 1996). Proportional stock density compares the number of fish of quality size (> 12 inches for largemouth bass) to the number of bass of stock size (> 8 inches in length), and is calculated by the formula: Number of bass 12 inches PSD = X 1 Number of bass 8 inches PSD is expressed as a percentage. A fish population with a high PSD consists mainly of larger individuals, whereas a population with a low PSD consists mainly of smaller fish. A value between 4 and 7 generally indicates a balanced bass population. Relative stock density (preferred, RSD 15 ) is the percentage of largemouth bass in a stock (fish over 8 inches) that are also 15 inches TL or longer, and is calculated by the formula: RSD 15 = Number of bass 15 inches X 1 Number of bass 8 inches An RSD 15 value between 1 and 4 indicates a balanced bass population, while values between 3 and 6 indicate a higher abundance of larger fish. As seen in Figure 6, these 1 years of data show a viable bass population, with 7 of 1 years having favorable PSD values, and 8 of 1 years having favorable RSD 15 values. The poorest stock density values (1992) reflect sampling conducted in the wake of Hurricane Andrew. 8

9 Percentage Percentage PSD RSD (preferred) Figure 6. Proportional stock density (PSD) and relative stock density (RSD 15 ) for largemouth bass collected from Henderson Lake, LA during fall electrofishing ( ). The last 9 years of stock density data (Figure 7) indicate that the Henderson Lake bass population is lacking in abundance of bass larger than 15 inches. The influence of environmental conditions is undoubtedly a significant contributing factor. Events occurring within this time frame include 3 major hurricanes, 2 floods, and a year of very low water levels PSD RSD (preferred) Figure 7. Proportional stock density (PSD) and relative stock density (RSD 15 ) for largemouth bass collected from Henderson Lake, LA during fall electrofishing (3 13). 9

10 Relative Weight (grams) Relative weight Mean relative weight (Wr) for each inch group is shown below in Figure 8. This measurement is defined as the ratio of fish weight to the weight of a standard fish of the same length. The Wr index is calculated by dividing the weight of a fish by the standard weight for its length, and multiplying the quotient by 1. Largemouth bass relative weights below 8 may indicate a problem of insufficient or unavailable forage; whereas relative weights closer to 1 indicate that sufficient forage is available. A description of the forage species and relative abundance is described below. Mean relative weights for almost all size classes of largemouth bass from Henderson Lake are at or above the 95 value. Relative weights for 12 and 13 were all near the 1 value. The robust body condition of Henderson Lake bass is an indication that bass forage is abundant and available Year Wr Substock (<8") Wr Stock (8"-12") Wr Quality (12"-15") Wr Preferred (15" +) Figure 8. The mean relative weights by length category for largemouth bass collected from fall electrofishing (3-13; n=1,259). Forage Henderson Lake forage is primarily comprised of shad and sunfish. An average of three 1- acre rotenone samples/year is shown below. The results provide an indication that forage has not been a limiting factor in largemouth bass growth. Table 1. Total weight (lbs.) of forage fishes collected from Henderson Lake, LA ( ). Year Total lbs./acre forage ,

11 Number of black crappie per hour Largemouth bass genetics Genetic analyses of largemouth bass through electrophoresis of liver tissues show a range of to 1% total Florida largemouth bass (FLMB) genome influence from the years 1999 and 4 (Table 2). Florida largemouth bass were stocked annually from to 6 at a rate of approximately 1 fish per acre. Despite the multiple stockings, genetic sampling conducted in 4 indicates that only 9% of the Henderson Lake bass population carried genetic material characteristic of Florida bass. Such results may be disappointing in terms of providing genetic potential for large bass size but, they are not entirely negative. The failure of a larger Florida bass influence provides additional confirmation that the native bass population is particularly resilient, and that recruitment is strong. Table 2. Genetic analysis of largemouth bass samples from Henderson Lake, LA (1999 and 4). Year Northern Florida Hybrid Florida Influence % % % % 4 91% 1% 8% 9% Black Crappie Relative abundance and size distribution- As shown in Figure 9, fall electrofishing CPUE for black crappie on Henderson Lake showed consistently lower numbers from 1988 through Hurricane Andrew struck in August of Fish kills related to Hurricane Andrew were massive. Increased abundance of sub-stock size (YOY) crappie in 1993 is evidence of fish population recovery from those kills. Diminished predation allowed high survival of newly spawned fish. A similar increase is noted in 3 following Hurricane Lili (Figure 1) Figure 9. The mean total CPUE (+ SE) for black crappie collected from Henderson Lake, LA during fall electrofishing ( ). 11

12 Number of black crappie per hour Number of black crappie per hour Figure 1. The mean total CPUE (+ SE) for black crappie collected from Henderson Lake, LA during fall electrofishing (3-13). Black crappie catch indices show consistently lower catch rates from with an increased number of stock-size crappie (5-8 inch) collected in 199 (Figure 11). The large increase in sub-stock and stock size crappie in 1993 indicates recovery from Hurricane Andrew related fish kills. The sharp increase in crappie collected in 3 shows that stock size fish (5-8 inch) were in relatively high abundance (Figure 12). The rise in sub-stock size fish in 9 indicates recovery after Hurricane Gustav. That cohort can be followed into the next year (1) with an increase in stock-size fish abundance Substock Stock Quality Preferred Figure 11. The CPUE for sub-stock, stock, quality, and preferred size black crappie collected from Henderson Lake, LA during fall electrofishing ( ). 12

13 Number of black crappie per hour Number of black crappie per hour Substock Stock Quality Preferred Figure 12. The CPUE for substock-, stock-, quality- and preferred-size black crappie collected from Henderson Lake, LA during fall electrofishing (3-13). Size distribution for black crappie in 13 is shown in Figure 13. The majority of fish collected were sub-stock (< 5 inches) with few fish from the quality (8-1 inch) or preferred size (1-12 inch) range. The total number of crappie collected in 13 (n=11), is greater than total catches from the last 7 years combined Inch Groups Figure 13. Size distribution for black crappie collected from Henderson Lake, LA in fall 13 (n=11). Sunfish Shoreline seine sampling is conducted to collect information related to species composition, year class strength, and prey availability. Henderson Lake sampling was conducted in summertime periods of, 1, and 5. All samples were conducted at night from 13

14 one-half hour after sunset until one half hour before sunrise. One quadrant haul, using a 25 foot x 6 foot seine, was conducted at each sampling station. A total of three samples were taken each year at three boat ramps, one per ramp. The quadrant haul was conducted by anchoring one end of the seine at the shoreline and the other stretched perpendicular to the shoreline. The distal end was then swept back around to the shoreline, keeping the lead line tight and on the bottom. After the seine haul is completed, all fish from the seine are placed in a plastic bag, properly marked, and placed on ice. Fish specimens were sorted to species, and by length. Total number of sunfish collected is provided in Table 3. Table 3. Sunfish collected from Henderson Lake, LA by seine haul from -5. YEAR TOTAL NUMBER CAUGHT 1, ,45 Commercial Commercial landings statistics are reported by parish and not by waterbody. As a result, landings data specific to Henderson Lake is not available. However, Henderson Lake has a thriving commercial fishery. Harvest includes crawfish, catfish, buffalo and freshwater drum. Aquatic invasive species Asian carp are present in Henderson Lake. They include the grass carp and the silver carp. Asian carp fish kills have been observed during periods of rapidly decreasing water level. Creel Surveys Angler creel surveys were conducted in, 1, and 5. The survey method used was an access point survey of completed fishing trips. Percent of total harvest by species is presented in Table 4. Table 4. The results of creel surveys conducted on Henderson Lake, LA, by year. Results are presented as the percent of total harvest of fish by species. SPECIES 1 5 AVERAGE Bluegill 34.9% 55.% 53.2% 45.5% Black Crappie 25.9% 14.9% 25.2% 23.6% White Crappie 23.% 6.6% 5.7% 13.5% Largemouth Bass 7.% 3.7% 4.1% 5.3% Warmouth 1.7% 2.2% 4.9% 3.% Redear Sunfish 1.7% 2.7% 2.9% 2.3% Freshwater Drum 1.% 8.1%.2% 2.% White Bass.5% 1.9%.7%.8% Blue Catfish.1% 1.4% 1.1%.7% Channel Catfish.4% 1.8%.2%.6% Yellow Bullhead.2%.% 1.3%.6% 14

15 Number of LMB from Interviews Buffalo 1.3%.%.%.6% Yellow Bass.4% 1.6%.%.5% Bowfin.6%.%.4%.4% Spotted Gar.8%.%.%.3% Spotted Sunfish.1%.2%.2%.1% Carp.2%.%.%.1% Black Bullhead.1%.%.%.% Smallmouth Buffalo.%.%.%.% Flathead Catfish.%.%.%.% An angler creel survey is currently in progress. This survey began July 1, 13 and is scheduled to continue through Dec. 31, 14. The survey method being used is an access point survey of completed fishing trips. The size distribution of angler harvested largemouth bass for the first six months (July 1, 13- Dec. 31, 13) is presented in Figure 14. The majority of fish harvested were in the 13 and 14 inch groups. During this time period, it is estimated that 24,29 largemouth bass were caught. Of those, 6,718 were harvested and 17,311 were released Inch Groups n = 338 Figure 14. The size distribution (inch groups) of angler harvested largemouth bass from Henderson Lake, LA for July 1 December 31, 13. HABITAT EVALUATION Aquatic Vegetation There is ongoing concern with overabundant aquatic vegetation in Henderson Lake. The primary species of concern are hydrilla (Hydrilla verticillata) and water hyacinth 15

16 (Eichhornia crassipes). Complaints related to boating access are common from fishermen, hunters, camp owners, and boat launch operators. Unfortunately, immediate relief is typically expected. However, the chemical used to control water hyacinth is a systemic herbicide. Systemic herbicides are effective, but a few days to several weeks may be required for complete plant mortality. The effects of systemic herbicides are directly related to plant metabolism, which is related to air temperature. Private boat landings as well as the public launch at the I-1 Butte La Rose Welcome Center are often cleared of water hyacinth only to have rafts of new plants block the ramps following a change in wind direction. At present there is approximately 5% coverage, or 25 acres of hydrilla in Henderson Lake as seen in Map 1 below. Other estimations made during the summer of 13 include approximately 3% coverage, or 15 acres of water hyacinth, and around 1 acres of giant salvinia (2% coverage). Giant salvinia was first detected in Henderson Lake in the fall of 12. Though eradication efforts were made, plants were observed again in 13. Biological treatments were applied in September 13 with the release of plant material containing giant salvinia weevils (Cyrtobagous salviniae). An estimated 19,36 adult weevils were released. As of July 14, LDWF spray crews have treated 1,477 acres of water hyacinth with 2,4-D, 63 acres of alligator weed with 2,4-D, 27 acres of common salvinia and 35 acres of giant salvinia with either a glyphosate/diquat mixture, or diquat depending on the time of year. During November 1 st -March 31 st, only diquat is used to spray salvinia species, while a glyphosate/diquat mixture is used from April 1 st -October 31 st based on the differences in plant metabolism and air temperatures. Also, 8 acres of pennywort were treated with 2,4-D. No contract spraying has been necessary thus far in 14. Triploid grass carp (TGC) were stocked in 14 (25, fish, 12+ inches in length) to assist with the ongoing hydrilla problem within the lake. The fish were certified as being triploid (sterile) by the U.S. Fish and Wildlife Service. 16

17 Map 1. Henderson Lake hydrilla coverage as of June,

18 CONDITION IMBALANCE / PROBLEM 1. In the absence of natural controls, invasive aquatic vegetation, including water hyacinth and hydrilla become overabundant each growing season. 2. Atchafalaya River water inundates Henderson Lake during high river flows. During a river flood pulse, water enters the control structure on the south end of the impoundment and then drains out of the same structure when the water later recedes. This hydrologic condition often creates a low dissolved oxygen situation and associated fish kills. CORRECTIVE ACTION NEEDED 1. Reduce overabundant vegetation through available means of control. In 13, LDWF met with officials from St. Martin Parish and the town of Henderson, LA and proposed a fall 13 drawdown. All parties were in favor of the proposed action. Mr. Guy Cormier, St. Martin Parish President, applied for a drawdown permit with the USACE in the summer of 13. This permit is required due to an Indian burial site that could be exposed with a reduction in water level. The permit was not issued because of the length of the permit process and a federal government shutdown. The LDWF recommended a drawdown for the fall of 14 and the St. Martin Parish Government applied for a permit. The permit was issued in August 14 and is valid for 5 years. A drawdown is scheduled for the fall of 14. LDWF will monitor problematic vegetation during the drawdown, evaluate its effectiveness, and make recommendations for future control efforts. 2. There are two solutions to the recurring fish kills in Henderson Lake. a. The first option would be for Henderson Lake to be completely separated from the Atchafalaya Basin and become a reservoir kept at pool stage with a structure that prohibits Atchafalaya flood waters from entering and draining from the southern end. The structure would need to be constructed with an overflow feature to allow rain water to drain from the lake and have the capability to conduct annual drawdowns for vegetation control. b. The second option would be to completely remove the control structure at the drain and have openings to the Atchafalaya River in the northern portion of the lake. This would allow Henderson Lake to fluctuate naturally with the river stage and have water flow from north to south through the system. The annual drying and flooding of Henderson Lake would then more closely mimic historical conditions. 18

19 RECOMMENDATIONS 1. Five consecutive years of summer/fall drawdowns are recommended for Henderson Lake. Previous efforts have proven that single year drawdowns have little effect on hydrilla in Henderson Lake. The southern control structure should be opened after the spring/summer flood cycle has fallen below 9 ft. MSL at the Butte La Rose gauge. The structure should remain open until the water level is 3 ft. below pool stage (6. ft. MSL). The dewatering rate should not exceed 4 inches per day. The 6. ft. MSL water level should be maintained as long as possible to achieve maximum potential. The heat from the summer months, as well as the possible freezing temps from the winter months, could provide a potential double impact to vegetative propagules during a drawdown. After the first drawdown, as many as 8-9% of hydrilla tubers in the bottom sediment will sprout, giving the false impression of failure. Consecutive drawdowns will be necessary to deplete hydrilla propagules in Henderson Lake. Natural water level fluctuation in the Mississippi/Atchafalaya Rivers will re-flood the lake during the winter and early spring months. 2. EPA approved herbicides will be applied to nuisance aquatic weeds in accordance with LDWF Aquatic Herbicide Procedure. Water hyacinth will be controlled with 2,4-D (.5 gal/acre) and a non-ionic surfactant (1 pint/acre). Both common salvinia and giant salvinia will be controlled with a mixture of glyphosate (.75 gal/acre) and diquat (.25 gal/acre) with Aqua King Plus (.25 gal/acre) and Air Cover (12 oz./acre) surfactants from April 1 to October 31. Outside of that time frame, diquat (.75 gal/acre) and a nonionic surfactant (.25 gal/acre) will be used. Sedge will be controlled with the aforementioned salvinia treatments if it is associated with those plants. If it is targeted specifically, 2,4-D will be used in conjunction with a non-ionic surfactant (1 pt./acre). 3. Standardized sampling will be conducted as per LDWF protocol. 4. Continue to work toward development of a comprehensive Henderson Lake Management Plan. Cooperative partners should include the St. Martin Parish Government, U.S. Fish & Wildlife Service, U.S. Army Corp of Engineers, LA Department of Natural Resources, U.S. Geological Survey, and LDWF. 5. Triploid grass carp retention will be monitored through LDWF standardized sampling. As a preliminary measure to reduce TGC escapement, an agreement with the St. Martin Parish government should be reached to limit control structure openings. 6. Continue to closely monitor and treat giant salvinia infestations as necessary. Giant salvinia weevil releases will continue on a routine basis. 19

20 REFERENCES Anderson, R. O., and R. M. Neumann Length, weight, and associated structural indices. Pages in B. R. Murphy and D. W. Willis, editors. Fisheries techniques, 2 nd edition. American Fisheries Society, Bethesda, Maryland.